Method and apparatus for heat treatment of particulates in an electrothermal fluidized bed furnace and resultant products

ABSTRACT

An electrothermal fluidized bed furnace is disclosed in which the furnace body has upper and lower cylindrical portions with the upper cylindrical portion having a diameter larger than that of the lower cylindrical portion. A conical portion is disposed below the lower cylindrical portion so that the conical portion and the lower cylindrical portion define a fluidizing zone while the upper cylindrical portion defines an overbed zone. A plurality of nozzles is disposed in the conical section for introducing fluidizing gas into the furnace, with the nozzles being arranged in a generally horizontal plan and orientated that the streams of the fluidizing gas introduced there through cross and form an upward flow in the central portion furnace body. Such an electrothermal fluidized bed furnace is adapted to be used in a continuous process for continuously heat treating of fine particulate matter.

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for thecontinuous high-temperature treatment in an electrothermally heatedfluidized bed of carbonaceous particles comprising fine or irregularlyshaped particles having a wide range of particle size distribution andthe products resulting from such treatment. More particularly, theinvention relates to, in one aspect, the use of a fountain-typefluidized bed for the high temperature treatment of carbonaceousparticles that cannot be effectively treated in a bubble-type fluidizedbed due to their fine sizes, range of size distribution, and shape.

It is known to use an electrothermal fluidized bed (EFB) furnace for thehigh temperature purification of carbonaceous materials and for hightemperature chemical synthesis (see U.S. Pat. Nos. 4,160,813 and4,547,430, respectively).

These processes use a fluidized bed furnace, as illustrated in U.S. Pat.No. 4,543,240, in which the cross-section of the fluidized bed portion(or “fluidizing zone”) of the EFB furnace is substantially constantalong its height and the fluidizing gas is introduced into the furnacethrough a multiplicity of generally vertically oriented gas nozzlesextending through a plate distributor at the bottom of the furnace. Thistype of EFB furnace is commonly referred to as a “bubble” EFB furnace.

The methods of purification and chemical synthesis using a bubble EFBfurnace have worked well for particles as small as 106 μm (140 mesh).However, bubble EFB furnaces have not performed well with respect tosmaller particles, particularly with those smaller than 75 μm (200mesh). Additionally, such furnaces are not effective for use withirregularly shaped particles such as flakes and needles, and or withparticles having a wide range of particle-size distribution(“polydispersed”), particularly where the material comprises a highcontent (greater than 30%) of fine particles with sizes less than 106 μm(140 mesh).

The use of bubble EFB furnaces to treat and/or synthesize polydispersedmaterials has resulted in the entrainment of particles smaller than 106μm (140 mesh). That is, the particles are entrained by the fluidizinggas outside of the active area of the EFB furnace. This results in a lowrecovery rate of treated product as a percent of raw material. This hasproven to be especially the case in bubble EFB furnaces where the rawmaterials are introduced at the top of the fluidized bed and the treatedparticles are discharged from the bottom of the furnace.

With respect to fine particles, particularly those smaller than 45 μm(325 mesh), and those of irregular shape, it has proven very difficult,or at times impossible, to uniformly fluidize such particles in a bubbleEFB furnace, because of channels of fluidizing gas. This is believed tobe due to the high adhesion forces between the small particles thatresult from the relatively large surface area for fine particles andalso because of stagnation zones formed in the bottom portion of thefluidized bed.

These shortcomings are the result of the particular hydrodynamics of abubble EFB furnace. In particular, the plate gas distributor and itsplurality of vertically oriented gas nozzles create a number of localcirculating zones that have an upward flow of particle/gas mixture and adownward flow of particles, with each zone being formed around a singlenozzle or group of nozzles on the distribution plate.

Accordingly, it is an object of the present invention to provide amethod for treating of fine, irregularly shaped and/or polydispersedparticulate matter in an electrothermal fluidized bed furnace. It is arelated object to provide a furnace for performing the method.

SUMMARY OF THE INVENTION

These objects, and others which will become apparent upon reference tothe following detailed description and drawing, are provided by anelectrothermal fluidized bed furnace in which the furnace body has upperand lower cylindrical portions, with the upper cylindrical portionhaving a diameter larger than that of the lower cylindrical portion. Aconical portion is disposed below the lower cylindrical portion so thatthe conical portion and the lower cylindrical portion define afluidizing zone while the upper cylindrical portion defines an overbedzone. The furnace includes at least one electrode extending through theupper and lower cylindrical portions and a treated material dischargepipe at the lower end of the conical portion. A feed pipe is providedfor introducing raw material into the lower cylindrical portion, and atleast one gas flue is provided at the top of the furnace body fordischarging fluidizing gas. A plurality of nozzles is disposed in theconical section for introducing fluidizing gas into the furnace, withthe nozzles being arranged in a generally horizontal plan and orientatedso that the streams of the fluidizing gas introduced therethrough crossand form an upward flow in the central portion furnace body.

Such an electrothermal fluidized bed furnace is adapted to be used in aprocess for continuously heat treating particulate matter bycontinuously introducing a non-reactive fluidizing gas through thenozzles of the furnace at pre-determined rate, continuously introducinguntreated particulate matter through the feed pipe of the furnace at apredetermined rate so that it forms a fluidized bed, energizing theelectrode so as to heat the fluidized bed, and continuously collectingthe treated particulate matter from the discharge pipe. Startingmaterials for the process advantageously include various types of cokes(e.g., fluid coke, flexi-coke, pitch coke, delayed coke and needle coke)and graphite materials (e.g., flake graphite, synthetic graphite,amorphous graphite, and vein graphite).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a fountain EFB furnaceaccording to the present invention.

FIG. 2 is a top view of the fountain EFB furnace of FIG. 1.

FIG. 3 is a cross-sectional view of the EFB furnace taken along line 3-3of FIG. 1, showing the fluidizing gas distribution nozzles.

FIG. 4 is similar to FIG. 3, except that it shows an alternativearrangement for the fluidizing gas distribution nozzles.

DESCRIPTION OF THE PREFERRED EMOBODIMENT

Turning to the figures of the drawings, there is seen a fountain-typeEFB furnace, generally designated 10, in accordance with the presentinvention. The principal characteristic of a fountain fluidized bed(also known as a “spout” or “jetting” fluidized bed) is that it has astrong circulating contour with a central upward flow of particle-gasmixture in the center of the fluidized bed and an outer downward flow ofparticles along the furnace walls. The high speed central upward flowdraws in and carries along the solid particles. The formation of fineparticle clusters and gas channels in the fluidized bed is avoided. Thevertical velocity gradient provides for a thorough fluidization of allfractions of poly-dispersed grain materials.

With reference to FIG. 1, the furnace 10 includes a furnace shell 11,typically made of steel that encases a furnace body 12. If the operationtemperature of the furnace is greater than 1500° C., made of graphiteand constitutes the return electrode. The furnace body may be made ofother materials if the operation temperature is less than 1500° C. Aninsulating material 14 is disposed between the shell 11 and body 12. Thefurnace body 12 comprises a lower cylindrical portion 16, an uppercylindrical portion 18 disposed above the lower cylindrical portion andhaving a larger diameter than the central cylindrical portion 16. (Forthe purposes of the description of the furnace 10, the term“cylindrical” means having vertical wall(s) and a constant cross sectionthroughout its height.) A conical gas distributor 20 is disposed belowthe central cylindrical portion 16, and has a plurality of fluidizinggas distribution nozzles 22. The nozzles 22 are in fluid communicationwith a plenum 24 into which the fluidizing gas is introduced through aninlet 26. The conical gas distributor 20 defines a central angle α(alpha) of from 30° to 90°, and preferably of from 40° to 60°. In such afurnace body 12, the space above the gas distribution nozzles 22 to thetop of the lower cylindrical portion 16 generally define the fluidizedbed zone 28. The space above the fluidized bed zone, coincidinggenerally with the upper cylindrical portion 18, is known as the overbedspace or free board zone 30. In the furnace of the present invention,the operational height H_(FB) of the fluidized bed area 28 generallycoincides with the distance between the nozzles 22 and the upper end ofthe lower cylindrical portion 18. In order to prevent the formation of abubble fluidized area in the top portion of the fluidized bed zone 28,H_(FB) is preferably less than or equal to one and one-half to twice theinside diameter ID_(FB) of the lower cylindrical portion 16. The minimalheight of the free board or overbed space H_(ov.s) is preferably one andone-half times the height of the fluidized bed H_(fb) to ensure that anyentrained particles are separated from the gas flow and returned to thefluidized bed space of the furnace.

Preferably, each of the cylindrical portions 16, 18 and the conical gasdistributor 20 has a circular or an elliptical cross-section. Othershaped cross-sections (such as square, rectangular, octagonal, etc.) mayexhibit satisfactory hydro-dynamic characteristics. However, such shapesare practically unworkable due to the amount of thermal expansionencountered by the furnace during use.

An elongated electrode 32 extends into the furnace body 12 from the top34 through the upper and lower cylindrical portions 18, 16,respectively. The electrode 32 is preferably fabricated from anelectrically conductive, heat-resistant material such as graphite andmust be electrically isolated from furnace body 12. When a singleelectrode is used, it must be located centrally within the furnace bodyand aligned with a vertical axis Y thereof. Alternatively, a pluralityof electrodes may be used, in which case the electrodes are arrangedsymmetrically about the central axis Y.

A feed pipe 38 is provided for continuously supplying raw material intothe fluidized bed zone 28 of the furnace body 12. As illustrated, thefeed pipe 38 is vertically orientated and extends through the top 34 ofthe furnace body 12, down through the upper cylindrical portion 18, andhas its outlet adjacent to the wall either at or below the top of thelower cylindrical portion 16. As such, raw material is introduced fromthe feed pipe 38 into the fluidized bed, or at least at the top surfacethereof, in the area of the downward flow of solid particles beingcirculated in the fluidized bed. This results in easier loading of rawmaterial into the fluidized bed, reduces the likelihood of the untreatedparticles being entrained by the upward flow of fluidizing gas andcarried into the overbed space, and provides better mixing of thetreated and raw materials.

The bottom of the furnace body includes a discharge port 40 throughwhich effluent solids may be continuously withdrawn by gravity flow. Thedischarge port 40 depends from the conical gas distributor 20, with theinlet to the discharge port 40 generally coinciding with the apex of theconical gas distributor 20.

Gaseous effluent can be withdrawn through one or more exhaust pipes orgas flues 42 in the top 34 of the furnace body 12. This effluent gas canbe readily cleaned and treated to control particulate and gaseouspollutants as required.

In keeping with the invention, the conical gas distributor 20 includes aplurality of fluidizing gas inlet nozzles 22 (eight shown), throughwhich fluidizing gas is introduced into the furnace body 12. The nozzles22 are orientated radially to the center of the conical distributor 20so that fluidizing gas forms crossing sprays, with a strong uniformupward flow. As can be appreciated, the velocity at which the fluidizinggas exits the nozzles and the average gas velocity in the fluidized bedportion 16 depend on the particle size, density, and shape of thematerial being fluidized. In the context of the process of the presentinvention, the fluidizing gas is typically nitrogen, argon or othernon-reactive gas.

In one embodiment, best seen in FIG. 3, the nozzles 22 are arranged sothat their axes X are aligned radially, with the fluidizing gas beingdirected toward the center of the conical gas distributor 20.Alternatively, the nozzles 22 maybe orientated so that their axes X forman angle β of from 10 to 20° with respect to a tangent to the conicalgas distributor 20 at the location of the nozzle, as best seen in FIG.4. The arrangement of the nozzles 22 so that their axes X are generallytangential to nozzle circle provides for a rotation of the fluidizedbed, making it more stable and less sensitive to any deviation of theelongated electrode 32 from the central axis Y. This angle helps toprevent the fluidized particles from being brought into contact with theconical gas distributor 20 at high velocity, which could result in unduewear of the walls of the gas distributor 20 from abrasion.

In order to prevent the fluidizing gas from interfering or disruptingthe discharge of treated particles from the furnace 10, the nozzles 22are preferably disposed at a height H_(N) above the conjunction of thegas distributor 20 and the inlet to the discharge port 40. Preferably,H_(N) is from 0.5 to 0.75 of the total height H_(TC) of the conical gasdistributor 20, and more preferably from 0.6 to 0.65 H_(TC).

Each of the nozzles 22 has preferably a ring cross section perpendicularto its X axis at which is defined a free cross-sectional area. Thecross-sectional shape can be circular or can have another shape such asrectangular, oval etc. The sum of the free cross-sectional areas of thenozzles 22 should be from 0.15 to 0.5% of the cross-sectional area ofthe cylindrical portion of the fluidized bed, that is thecross-sectional area of the lower cylindrical portion 16. Preferably,the free cross-sectional area of the nozzles 22 should be between 0.25and 0.4% of the cross-sectional area of the fluidized bed.

From the foregoing, the method for treating fine particulate materialsin the inventive EFB furnace should be self-evident. First, untreatedparticulate material is continuously fed by gravity through the feedpipe 38 into the reaction zone of the EFB furnace 10. The untreatedparticulate material may comprise fine, irregularly shaped orpolydispersed materials. In pilot runs, the polydispersed material hascomprised particles sized from between 1.7 mm (12 mesh), and as small as5 μm. Further, the untreated particulate may be an electroconductive orsemiconductive material, such as carbonaceous materials like carbonblack, coke (fluid coke, flexi-coke, delayed coke, needle coke, pitchcoke, etc.), and graphite (flake graphite, synthetic graphite, veingraphite, amorphous graphite, etc.). The various cokes may be eithergreen or calcined, petroleum or metallurgical, and are widely availablefrom various sources. The graphites are available from Superior GraphiteCo. of Chicago, Ill., the assignee of the present application. Theuntreated particulate matter is discharged from the feed pipe 38 at thetop of, or just inside, the fluidizing zone in the downward flow ofparticles.

The material from the feed pipe is maintained in a fluidized state inthe region of the furnace corresponding approximately to the lowercylindrical portion 16, and electric current is passed through thefluidized bed to uniformly heat the material to a high temperature,typically from 2,200-2,400° C.

Treated particulate material is continuously withdrawn by gravitythrough the discharge pipe 40. The discharge rate is such that thetreatment time of the particulate material within the fluidized bed issufficient to result in the desired heat treatment or chemical reaction.In the use of the present EFB furnace, there is no need for mechanicaldevices or moving parts within the furnace 10.

After being discharged through the pipe 40, the treated material may becooled in a cooling chamber (not shown). Gaseous effluent can bewithdrawn through the gas flue 42 at the top 34 of the furnace body 12.This gaseous effluent can be readily cleaned and treated to controlpollutants to the extent required.

By use of the inventive EFB furnace and the heat treatment fineparticles, significantly better recovery rates (of 90.3% in pilot runs)for treated particulate have resulted, in contrast to the recovery rateswhen using the prior art, bubble-type EFB's, (in which the recovery rateis typically less than 64%). In addition, the critical velocity offluidization has been reduced over that of a bubble-type EFB furnace by10-15%, for example from approximately 0.30 ft./sec. to approximately0.25 ft./sec. in the inventive EFB furnace.

Table I below compares purity characteristics for several differentgraphite and coke materials both prior to and after heat treatmentaccording to the present invention. The purity characteristics comparedare percentage (wt.) of ash and sulfur. TABLE I Purity of VariousCarbonaceous and Graphitic Thermally Processed Materials Material SulfurDescription Ash Content % Content % Flake Graphite Feed 0.9-1.15 —(Coarse) Treated 0 — Flake Graphite Feed 1.5-1.65 0.03-0.04 (Fine)Treated 0 0.0012 Fluid Coke Feed 0.6-0.7  1.9-2.0 Treated 0 0.007 Carbon Feed — 0.48  (Pellets) Treated — 0.004 

Thus, an improved EFB furnace and method for the treatment of fineparticulates have been provided. While the invention has been describedin terms of a preferred embodiment and method, there is no intent tolimit it to the same. For example, the furnace and process is equallywell suited for chemically treating find particulates, in which case thefluidizing gas can be a reducing gas, such as carbon monoxide, hydrogen,methane, etc. Instead, the invention is defined by the scope of theappended claims.

1. An electrothermal fluidized bed furnace comprising: a furnace bodywith a first cylindrical portion having a height, a second cylindricalportion disposed above the first cylindrical portion and having adiameter larger than that of the first cylindrical portion, and aconical portion disposed below the first cylindrical portion, the firstcylindrical portion and conical portion defining a fluidizing zone, andthe second cylindrical portion defining an overbed zone; at least oneelectrode disposed within the furnace body and extending through thefirst and second cylindrical portions; a treated material discharge pipeat the lower end of the conical portion; a raw material feed pipe forintroducing raw material into the first cylindrical portion; at leastone gas flue at the top of the furnace body for discharging fluidizinggas; and a plurality of nozzles disposed in the conical section forintroducing fluidizing gas into the furnace, the nozzles being arrangedin a generally horizontal plane and the nozzles being orientated so thatstreams of fluidizing gas introduced therethrough cross and form anupward flow in the central portion of the furnace body.
 2. Theelectrothermal fluidized bed furnace of claim 1 wherein the electrodehas a distal end and the distal end is located within the firstcylindrical portion of the furnace body.
 3. The electrothermal fluidizedbed furnace of claim 1 comprising a single electrode extending centrallythrough the furnace body.
 4. The electrothermal fluidized bed furnace ofclaim 1 comprising a plurality of electrodes extending through thefurnace body and arranged symmetrically about the central axis thereof.5. The electrothermal fluidized bed furnace of claim 1 wherein theconical portion defines a central angle of from 30° to 90°.
 6. Theelectrothermal fluidized bed furnace of claim 1 wherein the conicalportion defines a central angle of from 40° to 60°.
 7. Theelectrothermal fluidized bed furnace of claim 1 wherein each nozzle isarranged so that the stream of fluidizing gas enters the conical portionat an acute angle with respect to a tangent to the wall of the conicalportion.
 8. The electrothermal fluidized bed furnace of claim 1 whereinthe nozzles have a central axis and the nozzles are oriented withrespect to the conical portion wall so that the axis of each nozzle anda tangent to the wall of the conical portion at the location of thenozzle defines an angle of from 10° to 20°.
 9. The electrothermalfluidized bed furnace of claim 1 wherein the conical section has a totalheight H_(TC), and the nozzles are disposed in the conical section at adistance above the bottom of the conical section of from 0.5 H_(TC) to0.75 H_(TC).
 10. The electrothermal fluidized bed furnace of claim 1wherein the nozzles are disposed in the conical section at a distanceabove the bottom of the conical section of from 0.6 H_(TC) to 0.6H_(TC).
 11. The electrothermal fluidized bed furnace of claim 1 whereinthe fluidized bed zone has a height that is less than or equal to twicethe height of the first cylindrical portion.
 12. The electrothermalfluidized bed furnace of claim 1 wherein each nozzle has a ringcross-sectional area and the sum of the ring cross-sectional areas ofthe nozzles is from 0.15% to 0.5% of the cross-sectional area of thefirst cylindrical portion of the furnace body.
 13. The electrothermalfluidized bed furnace of claim 1 wherein each nozzle has a ringcross-sectional area and the sum of the ring cross-sectional areas ofthe nozzles is from 0.25% to 0.4% of the cross-sectional area of thefirst cylindrical portion of the furnace body.
 14. In an electrothermalfluidized bed furnace comprising a furnace body with a first cylindricalportion having a height, a second cylindrical portion disposed above thefirst cylindrical portion and having a diameter larger than that of thefirst cylindrical portion, and a conical portion disposed below thefirst cylindrical portion, the first cylindrical portion and conicalportion defining a fluidizing zone, and the second cylindrical portiondefining an overbed zone; at least one electrode disposed within thefurnace body and extending through the first and second cylindricalportions; a treated material discharge pipe at the lower end of theconical portion; a raw material feed pipe for introducing raw materialinto the first cylindrical portion; at least one gas flue at the top ofthe furnace body for discharging fluidizing gas; the improvementcomprising: a plurality of nozzles disposed in the conical section forintroducing fluidizing gas into the furnace, the nozzles being arrangedin a generally horizontal plane and the nozzles being oriented so thatstreams of fluidizing gas introduced therethrough cross and form anupward flow in the central portion of the furnace body.
 15. Theelectrothermal fluidized bed furnace of claim 14 wherein the electrodehas a distal end and the distal end is located within the firstcylindrical portion of the furnace body.
 16. The electrothermalfluidized bed furnace of claim 14 comprising a single electrodeextending centrally through the furnace body.
 17. The electrothermalfluidized bed furnace of claim 14 comprising a plurality of electrodesextending through the furnace body and arranged symmetrically about thecentral axis thereof.
 18. The electrothermal fluidized bed furnace ofclaim 14 wherein the conical portion defines a central angle of from 30°to 90°.
 19. The electrothermal fluidized bed furnace of claim 14 whereinthe conical portion defines a central angle of from 40° to 60°.
 20. Theelectrothermal fluidized bed furnace of claim 14 wherein each nozzle isarranged so that the stream of fluidizing gas enters the conical portionat an acute angle with respect to a tangent to the wall of the conicalportion.
 21. The electrothermal fluidized bed furnace of claim 14wherein the nozzles have a central axis and the nozzles are orientedwith respect to the conical portion wall so that the axis of each nozzleand a tangent to the wall of the conical portion at the location of thenozzle defines an angle of from 10° to 20°.
 22. The electrothermalfluidized bed furnace of claim 14 wherein the conical section has atotal height H_(TC), and the nozzles are disposed in the conical sectionat a distance above the bottom of the conical section of from 0.5 H_(TC)to 0.75 H_(TC).
 23. The electrothermal fluidized bed furnace of claim 14wherein the nozzles are disposed in the conical section at a distanceabove the bottom of the conical section of from 0.6 H_(TC) to 0.6H_(TC).
 24. The electrothermal fluidized bed furnace of claim 14 whereinthe fluidized bed zone has a height that is less than or equal to twicethe height of the first cylindrical portion.
 25. The electrothermalfluidized bed furnace of claim 14 wherein each nozzle has a ringcross-sectional area and the sum of the ring cross-sectional areas ofthe nozzles is from 0.15% to 0.5% of the cross-sectional area of thefirst cylindrical portion of the furnace body.
 26. The electrothermalfluidized bed furnace of claim 14 wherein each nozzle has a ringcross-sectional area and the sum of the ring cross-sectional areas ofthe nozzles is from 0.25% to 0.4% of the cross-sectional area of thefirst cylindrical portion of the furnace body.
 27. A process for thecontinuous treatment of particulate matter comprising: providing anelectrothermal fluidized bed furnace in accordance with claim 1;continuously introducing fluidizing gas through the nozzles of thefurnace at a predetermined rate; continuously introducing untreatedparticulate material through the feed pipe of the furnace at apredetermined rate so that the particulate matter forms a fluidized bedprincipally within the first cylindrical portion of the furnace;energizing the electrode so as to heat the fluidized bed; andcontinuously collecting treated particulate matter from the dischargepipe of the furnace.
 28. The method of claim 27 wherein the untreatedparticulate matter has a particle size smaller than 180 μm (80 mesh).29. The method of claim 27 wherein the untreated particulate mattercomprises carbonaceous materials.
 30. The method of claim 27 wherein theuntreated particulate matter comprises graphite selected from the groupcomprising flake graphite, synthetic graphite, amorphous graphite, andvein graphite.
 31. The method of claim 27 wherein the untreatedparticulate matter comprises coke selected from the group comprisingfluid coke, flexi-bed coke, pitch coke, delayed coke, and needle coke.32. The method of claim 27 wherein the untreated particulate mattercomprises an electroconductive or semiconductive material.
 33. A productresulting from the treatment of particulate coke selected from the groupcomprising fluid coke, flex-bed coke, pitch coke, delayed coke andneedle coke in accordance with the method of claim
 27. 34. A productresulting from the treatment of particulate graphite selected from thegroup comprising flake graphite, synthetic graphite, amorphous graphiteand vein graphite in accordance with the method of claim 27.